Dampers are hydraulic devices used to restrict the number of cyclic oscillations caused by a deflection force; damping forces are generated by pumping fluid through regulating orifices, converting kinetic energy into laminar and turbulent friction. Two types of damping devices are currently in wide use; telescopic and rotary vane type. Traditional van type rotary dampers have inherent disadvantages, including the following:                1. Hysteresis, due to disproportionate vane and shaft seal pre-load; caused by means such as compression springs, Elastomers, band springs or Elastomer Composites, resulting in frictional losses and limited dynamic range;        2. A rotary vane damper housing is subject to hoop stress, compression deformation and bending strain at vane junctions, causing excessive bypass flow and subsequent loss of compression; and        3. Thermal hysteresis due to non-uniform coefficient of expansion; exasperated by long sealing contours of the vane and structural components, leading to unpredictable sealing properties at higher temperatures and friction at lower temperatures. This limits the operating temperature range and diminishes the damping characteristics during thermal cycles. Furthermore, such prior art devices are hampered by their relative complexity, weight and high cost.        
The following U.S. patents disclose rotary dampers believed to be representative of the current state of the prior art: U.S. Pat. No. 4,926,984, issued May 22, 1990, U.S. Pat. No. 5,577,761, issued Nov. 26, 1996, U.S. Pat. No. 5,324,065, issued Jun. 28, 1994, U.S. Pat. No. 4,886,149, issued Dec. 12, 1989, U.S. Pat. No. 5,400,878, issued Mar. 28, 1995, U.S. Pat. No. 5,381,877, issued Jan. 17, 1995, and U.S. Pat. No. 6,296,090, issued Oct. 2, 2001.
Telescopic piston dampers are well known constructions employing a pressurized chamber or cylinder having a piston movable therein under controlled conditions and a piston rod associated therewith to provide the transfer of dampening force. These traditional-type dampers have certain fundamental drawbacks as well. In such devices, due to the fact that the piston rod passes through one end of the damper, there is a dynamic internal pressure differential due to rod volume inclusion, necessitating measures to counter the rod volume by either pressurizing the opposing chamber by means of highly compressed gas and a dividing piston, as in a monotube gas design, or a secondary chamber, via a foot valve, as in the known double-tube design, or by inclusion of a complimentary dummy shaft to equalize internal volume. All of the above measures reduce damping efficiency, add cost, complexity and weight as well as require substantial space.
Since telescopic dampers, to conform to non-linear elasto-kinematics motion of the associate elements, are deployed predominantly with translational mechanisms, they can not be installed directly, or fixedly to a haul or a chassis. This curtails the thermal conductance capacity of the damper and of the fluid. Under severe operating conditions, fluid temperature can rise to well over 100 degrees C., resulting in localized fluid vaporization and creation of gas pockets, known as Cavitation. At higher temperatures, damping forces diminish exponentially due to fluid viscosity reduction, giving higher orifice discharge coefficient. Also, conventional translational or linear dampers have limitations when applied to long travel functions. It is difficult to accommodate a large travel due to the danger of bucking the damper shaft, especially at high relative velocities, the linear space claim required by the length of a linear damper can also create packaging problems.
Functionally, in order to achieve the desired damper force-velocity characteristics, it is very difficult to adjust the piston-valve; solutions such as a hollow piston rod containing an internal shaft that performs the adjustments being very costly and often incompatible with servo controls due to high torque demands. Piston embedded servo valves are also complex, as well as reducing the hydraulic capacity of the damper.
As described earlier, to adapt to non-linear and elasto-kinematic requirements of the damping structures, telescopic dampers are predominantly deployed via translational bushings, excluding the possibility of direct attachment of damper to the structures, hence impeding a heat transfer passage.
My U.S. Pat. No. 5,971,118, issued Oct. 26, 1999, discloses a motion dampening apparatus which includes a damper housing defining a curved damper housing interior for a fixed attachment to a first structural member and a curved damper element for a fixed attachment to a second structural member and movable within the curved damper housing interior along a curved path of movement.
While the prior art indicated above does not teach or suggest the combination of structural features disclosed and claimed herein, it demonstrates the viability of the novel concept of transition of a force-bearing piston within a radial or circular structure; it also teaches the importance of fixed attachment of a damper to its associate structural members resulting in a thermally conducting pathway between a damper and a structure, as well as eliminating the use of translational bushings from the damper mounting points, which are also a source of parasitic friction.